Can IP Addresses be Replicated?

I've been dealing with a few hackers on my server lately. I caught one person hacking into other player's accounts. He says he didn't do this and tried to explain to me that his IP address was replicated by someone else and then that hacker used it to gain access to the accounts on the server and then griefed everything. I'm using Hamachi not just because I don't have to port forward, but also because of the extra security benefits. Here's a site that describes its security: https://secure.logmein.com/products/hamachi2/security.aspx
So is it actually possible that these Hamachi IP addresses can be replicated?

 

first of all is your server in offline-safemode=false? if so this is your problem

 

Short answer - No, it is not possible to replicate an IP address or a Hamachi IP (every Hamachi IP is assigned by their server and when the client launches Hamachi their MAC ID is compared with the one on record, if it doesn't match it gives them a new IP).

 

You can spoof ip addresses, just the chance of someone actually doing that's not very likely. You can likewise do this with your mac address though to a slightly lesser extent. As for hamachi haven't quite a clue how secure it actually is, there are ways to obtain an old hamachi ip or create new ones if you really wanted to. At any rate, the overall likelihood of any of this happening to a specific person is quite slim, generally easier to believe that they're lying than the possibility of a consipiracy being carried out against them.